The present invention relates to a branched polyvinyl imidazoline acid salt, a polymeric flocculant comprising the branched polyvinyl imidazoline acid salt, and a process for preparing the branched polyvinyl imidazoline acid salt.
Polymeric flocculants are used in waste water treatment, such as sewage treatment, excrement treatment, and that in the food industry, the paper and pulp industries, and various other industries. A polymeric flocculent is added to and mixed with sludge occurring after bioremediation of waste water to form flocs. After separation of the solids and liquid, the resulting cake is dehydrated. The dehydrated cake is burned or dumped for disposal. Recent years have seen the trend that sludge from waste water treatment, especially sewage treatment, is difficult to flocculate and dehydrate, for reasons such as the extension of a sludge transport pipe due to improvement in the living standard and integration of treatment facilities. As a result, the water content of the dehydrated cake increases, the volume of the dehydrated cake increases, and the cost for treatment, such as incineration cost, increases. Environmental problems also arise, such as increases in the amount of a carbon dioxide gas in accordance with increases in the amounts of fuel oils necessary for incineration. To solve these problems, a demand is growing for polymeric flocculants with excellent dehydration performance.
The properties of polymeric materials depend heavily on their constituent units, molecular weight, molecular weight distribution, and degree of branching. In polymeric materials used as polymeric flocculants, in particular, their performance as polymeric flocculants is known to be markedly improved by increasing their constituent units and molecular weights.
Polyvinyl imidazoline and/or its acid salt have or has been put to uses as flocculants (Japanese Patent Publication No. Sho 42-9653). However, when such a compound is used as a flocculant, especially as a polymeric flocculent for organic sludge for use in sewage treatment, its performance is not necessarily sufficient. To overcome this drawback, a polymeric flocculant comprising a novel copolymer has been proposed (Japanese Unexamined Patent Publication No. 2000-191733), but its performance as a polymeric flocculent has not been improved sufficiently.
As discussed above, acid salts of polyvinyl imidazoline have not exhibited sufficient performance when used as polymeric flocculants in waste water treatment, especially sewage treatment. In waste water treatment, especially in sewage treatment, sludge resulting from bioremediation tends to be flocculated and dehydrated with difficulty. This leads to increases in the water content of the dehydrated cake, the volume of the dehydrated cake, and the cost for treatment, such as incineration cost. There are also environmental problems, such as increases in the amount of a carbon dioxide gas in accordance with increases in the amounts of fuel oils necessary for incineration. Thus, there is an intense demand for polymeric flocculants for decreasing the water content of dehydrated cake in the treatment of sludge having a tendency toward difficult flocculation and dehydration.